WO2019153217A1

WO2019153217A1 - Method for recovering high-performance carbon fiber from inorganic cementing material

Info

Publication number: WO2019153217A1
Application number: PCT/CN2018/075922
Authority: WO
Inventors: 朱继华; 苏玫妮; 陈丕钰
Original assignee: 深圳大学
Priority date: 2018-02-09
Filing date: 2018-02-09
Publication date: 2019-08-15
Also published as: CN109153051A

Abstract

A method for recovering high-performance carbon fiber from an inorganic cementing material, comprising the following steps: (A) placing a carbon fiber-reinforced inorganic (cement-based) composite material in an electrolyte at a reaction temperature of 25°C-75°C, the electrolyte containing 0.5%-3% by weight percent of NaCl and 1.0 g/L-5 g/L of a catalyst; (B) energizing the carbon fiber-reinforced cement-based composite material placed in the electrolyte, the carbon fiber reinforced cement-based composite material connecting to a positive electrode of a power source, and controlling the current density to be 3333.3-6666.7 mA/m²; and (C) after reacting by energizing for 0.5-200 hours, extracting a produced carbon fiber recovered product from the electrolyte.

Description

Method for recovering high performance carbon fiber from inorganic cementitious material

Technical field

The present invention relates to the recovery and reuse of carbon fibers, and more particularly to a method for recovering high performance carbon fibers from inorganic cementitious materials.

Background technique

Carbon fiber has the advantages of high tensile strength, high Young's modulus, strong corrosion resistance, inert atmosphere resistance to ultra high temperature, excellent electromagnetic wave shielding, good biocompatibility and soft plasticity. After more than half a century of development, carbon fiber preparation technology has developed a wide variety of carbon fiber materials such as viscose carbon fiber, polyacrylonitrile fiber (PAN), asphalt fiber, polybenzimidazole fiber and polyester fiber.

Carbon Fiber Reinforced Plastic (CFRP) is a composite material made of carbon fiber as a reinforcement and an organic epoxy resin as a matrix. CFRP has the advantages of light weight, corrosion resistance and high tensile strength, and it is widely used in aerospace, industrial manufacturing and sporting goods. In 2012, the world's carbon fiber demand was 43,500 tons, and it is predicted to reach 130,000 tons in 2020.

In the field of civil engineering, CFRP can be cured by organic epoxy resin cementing material, pasted or placed on the surface or inside of the structure to improve the structural bearing capacity. The epoxy resin gel contains a plurality of polar groups and an active epoxy group, and the epoxy cured product has a large cohesive strength, so the bonding strength is high. However, due to the aging resistance, corrosion resistance and heat and humidity resistance of epoxy resin, anti-stripping, anti-cracking and impact resistance are not high. Since the 1990s, inorganic cementing materials have also been used in civil engineering, such as Cement-based materials such as modified cement paste, mortar and/or concrete, or base hair materials, etc., are bonded to CFRP to form a carbon fiber-reinforced inorganic (cement-based) composite material, thereby reinforcing the building structure. The inorganic cementitious material has excellent mechanical properties such as excellent corrosion resistance, high strength and toughness, and is well bonded to traditional civil engineering structural materials such as cement or concrete. Therefore, the reinforcing material (CFRP) and the original structure can work together and the reinforcing performance. better.

However, the wide application of high-performance fiber composite materials such as CFRP in the civil engineering field has also brought about extremely serious construction waste disposal problems. At the same time, high-performance fiber reinforced composites still maintain good performance after the end of life, and have high economic value. It is of great economic and social significance to realize the recovery and reuse of high-performance fiber reinforced composite materials. However, after the CFRP used for the reinforcement of the cement-based cementitious material structure is removed, the inorganic waste material such as cement which is difficult to peel off adheres to the construction waste of the carbon fiber material, and the treatment is more difficult.

Regarding the research on the recovery and application of fiber reinforced composite waste, a large number of scholars and institutions have participated in it. Foreign countries, especially Europe, the United States and Japan, have begun to carry out fiber reinforced composite wastes with the advance of their industries and technologies. Recycling and reuse research. However, various existing carbon fiber recovery methods are directed to epoxy resin adhesives as the matrix material and cementitious materials, and carbon fiber recovery studies for carbon fiber reinforced inorganic composite materials have not been publicly reported.

In view of this, the present invention provides a method for recovering high-performance carbon fiber from inorganic cementitious materials which is technically feasible, simple in operation, high in economic efficiency and environmental protection, and is not only beneficial for recycling and reuse of carbon fiber materials, but also can solve construction. The problem of garbage disposal has important economic and social significance.

Summary of the invention

The main object of the present invention is to provide a method for recovering high-performance carbon fiber from an inorganic cementing material, wherein the carbon fiber recycling method provided by the invention has the advantages of simple process steps, low difficulty, high recovery rate, low cost and low fiber damage. Etc.

Another object of the present invention is to provide a method for recovering high-performance carbon fibers from an inorganic cementing material, wherein the carbon fiber recovery method provided by the present invention can not only recover carbon fibers, but also simultaneously recover resin materials and decompose inorganic gelation. Materials, in order to reduce the difficulty of handling construction waste containing CFRP, and to maximize the recycling and reuse of carbon fiber reinforced cement-based composite waste, have significant environmental value and important social significance.

Another object of the present invention is to provide a method for recovering high-performance carbon fibers from an inorganic cementing material, wherein the carbon fiber recovery method provided by the present invention has low toxicity, low requirements on production equipment, and reaction conditions. mild. The carbon fiber recovery method provided by the present invention does not require shearing and/or crushing treatment of the carbon fiber reinforced composite material, and therefore, materials of any size can be recovered. At the same time, it is not necessary to shear and/or crush the carbon fiber reinforced composite material, and the mechanical properties of the recovered carbon fiber material are hardly damaged, and the economic value of the recovered carbon fiber material is higher.

Another object of the present invention is to provide a composition for recovering high performance carbon fibers from an inorganic cementitious material.

Other advantages and features of the invention will be apparent from the description and appended claims appended claims

According to the present invention, a method for recovering high performance carbon fibers from an inorganic cementitious material capable of achieving the foregoing and other objects and advantages includes the following steps:

(A) placing a carbon fiber-reinforced inorganic (cement-based) composite material in an electrolyte at a reaction temperature of 25 ° C to 75 ° C, wherein the electrolyte contains 0.5% to 3% by weight of NaCl and 1.0 g/L to 5 g. /L catalyst;

(B) energizing the carbon fiber reinforced cement-based composite material placed in the electrolyte, wherein the carbon fiber reinforced cement-based composite material is connected to the positive electrode of the power source, and the current density is controlled to be 3333.3 to 6666.7 mA/m ² , wherein the current density is The size is calculated according to the surface area of the carbon fiber reinforced inorganic (cement-based) composite material in which the carbon fiber material is immersed in the electrolyte; and

(C) After the energization reaction was carried out for 0.5 to 200 hours, the produced carbon fiber recovered product was taken out from the electrolytic solution.

In an embodiment, wherein the step (C) further comprises the step of:

(D) Flushing the carbon fiber reclaimed material taken out from the electrolyte to remove the inorganic (cement-based) gel material.

In an embodiment, wherein the carbon fiber recyclate surface is provided with spaced apart pores according to step (D).

In an embodiment, wherein according to step (D), the interval between each of the holes is greater than 0.1 mm, the flushing water pressure is higher than 0.1 MPa, and the rinsing time is not less than 3 seconds.

According to a preferred embodiment of the present invention, the present invention further provides an electrolyte for recovering high performance carbon fibers from an inorganic cementitious material, comprising:

0.5% to 3% NaCl;

1.0 g/L to 5 g/L of HNO ₃ ; and

80% to 98% water.

Further objects and advantages of the present invention will be fully realized from the understanding of the appended claims.

These and other objects, features and advantages of the present invention will become apparent from

DRAWINGS

Figure 1A shows a schematic structural view of a carbon fiber electrochemical recovery system.

1B and 1C are schematic views showing the structure of a carbon fiber reinforced cement-based composite test piece.

Figure 2 shows a carbon fiber recyclate recovered from a carbon fiber reinforced cementitious composite.

Figure 3A shows the interface between the cementitious and carbon fibers of a carbon fiber reinforced cementitious material that has not been electrochemically recycled.

Figure 3B shows a detail enlargement of the portion of the block in Figure 3A.

Figure 3C shows the interface between the cementitious material of the carbon fiber recyclate and the carbon fiber.

Figure 3D shows a detail enlargement of the portion of the block in Figure 3C.

Figure 4 shows the amount of carbon fiber recovered from samples of different grouped carbon fiber reinforced cementitious composites.

Figure 5 shows the voltages of different groups of carbon fiber reinforced cementitious composite samples during the reaction.

Figure 6 shows the tensile strength of carbon fiber monofilaments recovered from different groups of carbon fiber reinforced cementitious composite samples.

Figure 7 shows the interfacial shear strength of recycled carbon fibers from different grouped carbon fiber reinforced cementitious composite samples.

Figure 8A shows the surface failure mode of the carbon fiber precursor.

Figure 8B shows the surface failure mode of the carbon fiber recovered from the I20S _2.0 H ₁ carbon fiber reinforced cementitious composite sample.

Figure 8C shows the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₁ carbon fiber reinforced cementitious composite sample.

Figure 8D shows the surface failure mode of the carbon fiber recovered from the I20S _2.0 H ₃ carbon fiber reinforced cementitious composite sample.

Figure 8E shows the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₃ carbon fiber reinforced cementitious composite sample.

Figure 8F shows the surface failure mode of the carbon fiber recovered from the I20S _2.0 H ₅ carbon fiber reinforced cementitious composite sample.

Figure 8G shows the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₅ carbon fiber reinforced cementitious composite sample.

Figure 9A shows an SEM scan image of the surface of a carbon fiber precursor.

Figure 9B shows an SEM scan of the carbon fiber recovered from the I20S _2.0 H ₁ carbon fiber reinforced cementitious composite sample.

Figure 9C shows an SEM scan of carbon fiber recovered from a sample of I40S _2.0 H ₁ carbon fiber reinforced cementitious composite.

Figure 9D shows an SEM scan of the carbon fiber recovered from the I20S _2.0 H ₃ carbon fiber reinforced cementitious composite sample.

Figure 9E shows a SEM scan of the carbon fiber recovered from the I40S _2.0 H ₃ carbon fiber reinforced cementitious composite sample.

Figure 9F shows an SEM scan of the carbon fiber recovered from the I20S _2.0 H ₅ carbon fiber reinforced cementitious composite sample.

Figure 9G shows an SEM scan of the carbon fiber recovered from the I40S _2.0 H ₅ carbon fiber reinforced cementitious composite sample.

Figures 10A and 10B show AFM scan images of the surface of a carbon fiber precursor.

Figures 10C and 10D show AFM scan images of recovered carbon fibers from a sample of I20S _2.0 H ₁ carbon fiber reinforced cementitious composites.

10E and 10F show AFM scan images of recovered carbon fibers of a sample of I40S _2.0 H ₁ carbon fiber reinforced cementitious composite.

Figures 10G and 10H show AFM scan images of recycled carbon fibers from a sample of I20S _2.0 H ₃ carbon fiber reinforced cementitious composites.

10I and 10J show a table AFM scan image of the recovered carbon fiber of the I40S _2.0 H ₃ carbon fiber reinforced cementitious composite sample.

Figures 10K and 10L show AFM scan images of carbon fibers recovered from samples of the I20S _2.0 H ₅ carbon fiber reinforced cementitious composite.

Figure 10M and Figure 10N show AFM scan images of recycled carbon fibers from a sample of I40S _2.0 H ₅ carbon fiber reinforced cementitious composites.

Figure 11A shows an XPS (X-ray photoelectron spectroscopy) full spectrum image of the surface of a carbon fiber precursor.

Figure 11B shows an XPS scan C1s high resolution narrow spectrum image of the surface of a carbon fiber precursor.

Figure 11C shows an XPS-scan full-spectrum image of carbon fiber recovered from a sample of I20S _2.0 H ₁ carbon fiber reinforced cementitious composite.

Figure 11D shows an XPS scan C1s high resolution narrow-spectrum image of carbon fiber recovered from a sample of I20S _2.0 H ₁ carbon fiber reinforced cementitious composite.

Figure 11E shows an XPS-scan full-spectrum image of carbon fiber recovered from a sample of I20S _2.0 H ₃ carbon fiber reinforced cementitious composites.

Figure 11F shows a high resolution narrow-spectrum image of XPS scan C1s of carbon fiber recovered from a sample of I20S _2.0 H ₃ carbon fiber reinforced cementitious composite.

Figure 11G shows an XPS-scan full-spectrum image of the carbon fiber recovered from the I20S _2.0 H ₅ carbon fiber reinforced cementitious composite sample.

Figure 11H shows a high-resolution narrow-spectrum image of XPS scan C1s of carbon fiber recovered from I20S _2.0 H ₅ carbon fiber reinforced cementitious composite samples.

Figure 12 shows the amount of carbon fiber recovered from carbon fiber reinforced cementitious composite samples at different temperatures.

Figure 13 shows the voltage of a carbon fiber reinforced cementitious composite sample during the reaction at different temperatures.

Figure 14 shows the tensile strength of monofilaments of carbon fibers recovered from carbon fiber reinforced cementitious composite samples at different temperatures.

Figure 15 shows the interfacial shear strength of carbon fibers recovered from carbon fiber reinforced cementitious composite samples at different temperatures.

Figure 16A shows the surface failure mode of carbon fiber recovered from a sample of I20S _2.0 H ₃ T ₁ carbon fiber reinforced cementitious composite.

Figure 16B shows the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₁ carbon fiber reinforced cementitious composite sample.

Figure 16C shows the surface failure mode of the carbon fiber recovered from the I20S _2.0 H ₃ T ₂ carbon fiber reinforced cementitious composite sample.

Figure 16D shows the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₃ T ₂ carbon fiber reinforced cementitious composite sample.

Figure 16E shows the surface failure mode of the carbon fiber recovered from the I20S _2.0 H ₃ T ₃ carbon fiber reinforced cementitious composite sample.

Figure 16F shows the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₃ T ₃ carbon fiber reinforced cementitious composite sample.

Figure 17A shows an SEM scan of the carbon fiber recovered from the I20S _2.0 H ₃ T ₁ carbon fiber reinforced cementitious composite sample.

Figure 17B shows an SEM scan of the carbon fiber recovered from the I40S _2.0 H ₃ T ₁ carbon fiber reinforced cementitious composite sample.

Figure 17C shows an SEM scan of the carbon fiber recovered from the I20S _2.0 H ₃ T ₂ carbon fiber reinforced cementitious composite sample.

Figure 17D shows an SEM scan of the carbon fiber recovered from the I40S _2.0 H ₃ T ₂ carbon fiber reinforced cementitious composite sample.

Figure 17E shows a SEM scan of the carbon fiber recovered from the I20S _2.0 H ₃ T ₃ carbon fiber reinforced cementitious composite sample.

Figure 17F shows an SEM scan of the carbon fiber recovered from the I40S _2.0 H ₃ T ₃ carbon fiber reinforced cementitious composite sample.

Figure 18A shows an XRD scan of carbon fibers recovered from I20S _2.0 carbon fiber reinforced cementitious composite samples at different temperature gradients.

Figure 18B shows an XRD scan of carbon fibers recovered from I40S _2.0 carbon fiber reinforced cementitious composite samples at different temperature gradients.

Figure 19A shows an XPS-scan full-spectrum image of carbon fiber recovered from a sample of the I20S _2.0 H ₃ T ₁ carbon fiber reinforced cementitious composite.

Figure 19B shows a high resolution narrow-spectrum image of XPS scan C1s of carbon fiber recovered from a sample of I20S _2.0 H ₃ T ₁ carbon fiber reinforced cementitious composite.

Figure 19C shows an XPS-scan full-spectrum image of the carbon fiber recovered from the I20S _2.0 H ₃ T ₂ carbon fiber reinforced cementitious composite sample.

Figure 19D shows an XPS scan C1s high resolution narrow-spectrum image of carbon fiber recovered from a sample of I20S _2.0 H ₃ T ₂ carbon fiber reinforced cementitious composite.

Figure 19E shows an XPS-scan full-spectrum image of the carbon fiber recovered from the I20S _2.0 H ₃ T ₃ carbon fiber reinforced cementitious composite sample.

Figure 19F shows an XPS scan C1s high resolution narrow-spectrum image of carbon fiber recovered from a sample of I20S _2.0 H ₃ T ₃ carbon fiber reinforced cementitious composite.

Figure 20A shows an XRD scan of carbon fibers recovered from I20S _2.0 carbon fiber reinforced cementitious composite samples at various catalyst concentrations.

Figure 20B shows an XRD scan of carbon fibers recovered from I40S _2.0 carbon fiber reinforced cementitious composite samples at various catalyst concentrations.

Detailed ways

The following description is disclosed to enable any person skilled in the art to make and use the invention. The preferred embodiments provided in the following description are merely exemplary and modifications that are obvious to those skilled in the art, and are not intended to limit the scope of the invention. The general principles defined in the following description may be applied to other embodiments, alternatives, modifications, equivalents and applications without departing from the spirit and scope of the invention.

Referring to Figures 1A to 20B of the accompanying drawings, a method for recovering high performance carbon fibers from an inorganic cementitious material in accordance with a preferred embodiment of the present invention is described in detail, and an exemplary embodiment is explained using a carbon fiber reinforced cementitious material. The method wherein the method for recovering carbon fibers from a carbon fiber reinforced cement-based composite material (waste) comprises the steps of:

(A) placing a carbon fiber reinforced cement-based composite material in an electrolyte at a reaction temperature of 25 ° C to 75 ° C, wherein the electrolyte contains 0.5% to 3% by weight of NaCl and 1.0 g/L to 5 g/L. catalyst;

It is worth mentioning that in some embodiments of the method for recovering high-performance carbon fibers from the inorganic cementitious material of the present invention, the method for recovering high-performance carbon fibers from the inorganic cementing material is in the step (C). Then further steps are included:

(D) Flushing the carbon fiber reclaimed material taken from the electrolyte to remove the cement-based gel.

Further, in the step (D), wherein the surface of the carbon fiber recyclate is provided with spaced-apart holes, in particular, the interval between each of the holes is greater than 0.1 mm, the flushing water pressure is higher than 0.1 MPa, and the flushing is performed. The time is no less than 3 seconds. As used herein, electrolyte refers to the inclusion of NaCl, water, and a catalyst that is used to recover carbon fibers from a carbon fiber reinforced cementitious composite. Illustratively, the NaCl concentration is measured in weight percent, for example, the NaCl concentration may be x1 (0.5%), x2 (1%), x3 (2%), and x4 (3%). The current (I) size is measured in mA, such as 20 mA, 40 mA. In the example, when the thickness of the CFRP is ignored, the experimental surface area (A) of the CFRP test piece exposed to the electrolyte is 2 × 100 mm × 30 mm = 6000 mm ² , so the corresponding current density (i = I / A) is 3333.3, respectively. , 6666.7 mA / m ² . The grouping and experimental parameters of specific carbon fiber reinforced cement-based composites are shown in Table 5.1. The number of carbon fiber reinforced cement-based composite specimens is determined by the applied current intensity, NaCl concentration, HNO ₃ concentration and temperature, such as the test piece number “I20S”. _2.0 H ₃ T ₄₀ ”, the first part “I20” means that the constant current intensity applied by the test piece is 20 mA, and the second part “S _2.0 ” means that the concentration of NaCl in the electrolyte is 2% of the mass of deionized water, the third part "H ₃ " means that the concentration of HNO ₃ added per liter of the electrolyte is ₃ g/L. The fourth part "T ₄₀ " means that the temperature of the electrolyte is maintained at 40 ° C during the experiment. Without the fourth part, the test is carried out at room temperature (temperature is 25 degrees)

As shown in Figure 1A of the accompanying drawings, the (electrochemical) recovery system for recovering carbon fibers from CFRP reinforced cement-based composite materials includes a DC power source to provide a unidirectional operating current for the system; a cathode-anode material in which the carbon fiber reinforced cement base to be recovered The composite plate (recycled sample) is connected as an anode to the positive electrode of the power supply, the stainless steel piece is connected as a cathode to the negative electrode of the power source; the electrolyte contains NaCl, water (solvent) and a catalyst; the data log (Datalog) is connected in parallel with the recovered sample and the stainless steel piece. , monitor sample voltage changes. Illustratively, the carbon fiber reinforced cementitious composite panel is placed in parallel with the stainless steel sheet and the distance between the two is fixed at 50 mm.

As shown in Figure 2 of the accompanying drawings, the carbon fiber recovered material recovered from the carbon fiber reinforced cement-based composite material is soft in texture by point chemical treatment.

As shown in FIG. 3A and FIG. 3B of the drawings of the specification, the interface between the cement-based and carbon fibers of the carbon fiber reinforced cement-based material which is not electrochemically treated has a rib-shaped groove structure which is complete and regular and can form a strong bond with carbon fibers. The mechanical bite is used, the interface has only very small holes, and no cracks and other defects are visible.

As shown in FIG. 3C and FIG. 3D of the drawings of the specification, the regular rhombic groove structure of the interface between the cement-based material of the carbon fiber recyclate and the carbon fiber interface has been divided into broken small units by large cracks in the longitudinal and lateral directions. Fluffy, and there are many large crack holes in which the porosity increases sharply, the interface has completely lost the mechanical bite with carbon fiber, and the adhesion is greatly reduced.

As shown in Figure 4 of the accompanying drawings, the amount of carbon fiber recovered from different carbon fiber reinforced cement-based composite samples is different. The carbon fiber recovery increases first and then decreases with the increase of HNO ₃ concentration, and the concentration of HNO ₃ is 3g. At /L, the amount of carbon fiber recovered is the largest. In the HNO ₃ concentration of 1 g/L group, the amount of carbon fiber recovered was significantly reduced.

As shown in Figure 5 of the accompanying drawings, the voltage variation of different groups of carbon fiber reinforced cementitious composite samples during the reaction. Among them, the H ₀ group has the highest voltage and the highest relative fluctuation; the H ₅ group has lower voltage than the H ₀ group, but it is still relatively high; the H ₃ and H ₁ groups have lower sample voltages. In general, the I40 series sample voltage is larger than the I20 series, and the S _3.0 series sample voltage is larger than the S _2.0 series.

As shown in Figure 6 of the accompanying drawings, the tensile strength of carbon fiber monofilament recovered from different carbon fiber reinforced cementitious composite samples, wherein the tensile strength of the recovered carbon fiber decreases with increasing HNO ₃ concentration. In the trend of 0 to 3 (g/L) HNO ₃ concentration range, the tensile strength of carbon fiber decreases slightly, and the tensile strength of carbon fiber recovered is sharply decreased in the range of HNO ₃ concentration of 3 to 5 (g/L). .

As shown in Figure 7 of the accompanying drawings, the interfacial shear strength of carbon fibers recovered from different carbon fiber reinforced cementitious composite samples is reduced, and the interfacial shear strength of the recovered carbon fibers decreases with increasing HNO ₃ concentration, but The carbon fibers recovered from the H ₁ and H ₃ groups have greater shear strength than the original fibers.

As shown in Fig. 8A of the drawings of the specification, the surface failure mode of the carbon fiber precursor is DB.

As shown in Fig. 8B of the accompanying drawings, the surface damage mode of the carbon fiber recovered from the I20S _2.0 H ₁ carbon fiber reinforced cement-based composite sample is DB.

As shown in Figure 8C of the accompanying drawings, the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₁ carbon fiber reinforced cementitious composite sample is DB.

As shown in Fig. 8D of the accompanying drawings, the surface failure mode of the carbon fiber recovered from the I20S _2.0 H ₃ carbon fiber reinforced cement-based composite sample is CB.

As shown in Fig. 8E of the accompanying drawings, the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₃ carbon fiber reinforced cement-based composite sample is CB.

As shown in Fig. 8F of the drawings, the surface damage mode of the carbon fiber recovered from the I20S _2.0 H ₅ carbon fiber reinforced cementitious composite sample is CB.

As shown in Figure 8G of the accompanying drawings, the surface failure mode of the carbon fiber recovered from the I40S _2.0 H ₅ carbon fiber reinforced cement-based composite sample is EB.

As shown in Figure 9A of the accompanying drawings, the SEM scan image of the surface of the carbon fiber precursor shows that the surface is smooth.

As shown in Figure 9B and Figure 9C of the accompanying drawings, the carbon fiber surface of the I20S _2.0 H ₁ group and the I40S _2.0 H ₁ carbon fiber reinforced cement matrix composite sample was recovered except that a very small amount of cement gel was attached. Seeing defects such as crack cracks and pits is very complete.

As shown in Figure 9D and Figure 9E of the accompanying drawings, the carbon fiber surface of the I20S _2.0 H ₃ group and the I40S _2.0 H ₃ carbon fiber reinforced cement matrix composite sample is clean, and few cement gel particles remain, but A cross-crack is found on the surface of the carbon fiber of individual numbers, and a weak layer is formed at the crack, resulting in a decrease in the tensile strength of the carbon fiber.

As shown in Figure 9F and Figure 9G of the drawings, the carbon fiber surface of the I20S _2.0 H ₅ group and the I40S _2.0 H ₅ carbon fiber reinforced cement matrix composite sample is recovered, and many cement gel particles are found on the surface of the carbon fiber. Longitudinal cracks and transverse cracks, and the depth is not shallow, reducing the force cross section of the carbon fiber, so the tensile strength of the carbon fiber recovered by the H ₅ series is seriously degraded.

As shown in Figures 10A to 10N of the accompanying drawings, the AFM scan image of the carbon fiber recovered from each of the grouped carbon fiber reinforced cementitious composite samples shows that when the concentration of HNO ₃ is low, a small amount of oxidation of the electrochemical recovery process is shown. The etch will increase the interfacial shear strength of the carbon fiber, and when the HNO ₃ concentration is increased to a certain extent, the excessive oxidative etching reduces the interfacial shear strength of the carbon fiber.

As shown in Figures 11A to 11H of the accompanying drawings, XPS scanning full-spectrum images and C1s high-resolution narrow-spectrum images of carbon fibers recovered from samples of each group of carbon fiber reinforced cement-based composite materials show that carbon fiber has undergone a certain degree in the recovery process. Oxidation, surface oxygen content increases, surface activity is increased, and O~C=O bond appears, which greatly improves the chemical bonding ability of carbon fiber and epoxy resin; the oxygen-carbon ratio and functional group content of carbon fiber recovered from recovery It can be seen that when the concentration of HNO ₃ is 1 (g/L), the degree of oxidation of carbon fiber is too low. When the concentration of HNO ₃ is 3 (g/L), the degree of oxidation of carbon fiber is the best. Increasing the concentration of HNO ₃ is only to make the surface of carbon fiber C. The =O key increases.

As shown in Figure 12 of the accompanying drawings, the amount of carbon fiber recovered from the carbon fiber reinforced cement-based composite sample at different temperatures shows a high first and then a low temperature, and the carbon fiber is recovered at a temperature of 40 ° C. The largest amount.

As shown in Figure 13 of the accompanying drawings, the voltage of the carbon fiber reinforced cement-based composite sample during the reaction process at different temperature conditions indicates that the voltage of the carbon fiber reinforced cement-based composite sample is low, and the voltage difference values of different grouped samples are very high. Small, indicating that under high temperature conditions, the system resistance of the sample is very small, and the voltage of all samples is basically stable during the electrochemical recovery cycle.

As shown in Figure 14 of the accompanying drawings, the tensile strength of the monofilament of the carbon fiber recovered from the carbon fiber reinforced cementitious composite sample at different temperature conditions first decreases and then increases slowly.

As shown in Figure 15 of the accompanying drawings, the interfacial shear strength of carbon fiber recovered from carbon fiber reinforced cement-based composite samples with different temperature conditions increases first and then decreases and then decreases.

As shown in Fig. 16A to Fig. 16F of the accompanying drawings, the surface failure mode of the carbon fiber recovered from the sample of each group of carbon fiber reinforced cement-based composite materials, except that the failure mode of I40S _2.0 H ₃ T ₂ is CB, the failure mode of other samples Both are DB.

As shown in FIG. 17A to FIG. 17F of the drawings of the specification, the defects of the surface cracks of the carbon fiber obtained by the recovery of the sample of the carbon fiber reinforced cement-based composite materials are less, indicating that the recovery cycle is shortened to reduce the oxidation and corrosion of the recovery process.

As shown in FIG. 19A to FIG. 19F of the drawings of the specification, the XPS-scan full-spectrum image of the carbon fiber recovered from each of the grouped carbon fiber reinforced cementitious composite samples and the high-resolution narrow-spectrum image of the XPS scan C1s show that the temperature is higher than the normal temperature state T. ₀ (25 ° C), the oxygen introduced on the surface of the carbon fiber is more at high temperature; at the temperature of T ₁ (40 ° C), the oxygen content on the surface of the recovered carbon fiber and the strong hydrophilic functional group O~C=O content are the most. As the temperature continues to rise, there is a decrease; however, the content of C-Cl bond on the surface of carbon fiber is as high as 8.2%, which is subject to more serious chlorination, which causes the tensile strength and shear strength of carbon fiber to decrease to some extent.

Further, the present invention will be described in detail in conjunction with the following specific examples.

Example 1: Preparation of raw materials (carbon fiber reinforced cement-based composite)

The carbon fiber reinforced cement-based composite material of this experiment consists of two major parts, CFRP and cement-based cementitious materials.

The CFRP material is selected from the HITEX-C300 carbon fiber cloth produced by Nanjing Haituo Composite Materials Co., Ltd., which is a 12K unidirectional woven fabric with a density of 300g/m2. The cement is selected from the China Resources brand PO42.5R ordinary composite Portland cement produced in Dongguan. The silicon powder is a Siken silicon powder produced in Shanghai, and the high molecular polymer is a redispersible powder of the DY-5025 (Germany) model. The carbon fiber short yarn produced by Hong Kong Kaben Co., Ltd. is selected to have a length of about 3 mm. Sodium chloride (analytical grade) and HNO ₃ (analytical grade) produced by Xiqiao Chemical Co., Ltd. were selected. The mass fraction of sodium chloride was 99.5%, and the mass fraction of B was 65%-68%. In the carbon fiber reinforced cement-based composite material, the carbon fiber cloth is in the middle, and the specific composition and content of the cement-based material are shown in Table 1.1.

The carbon fiber reinforced cement-based composite test piece has a size of 30 mm × 245 mm × 4 mm. Along the thickness direction of the carbon fiber reinforced cementitious composite material, the cement material is about 2 mm thick on the upper and lower sides, and the carbon fiber cloth is in the middle, as shown in FIG. 1B and FIG. 1C. It is divided into three areas along its length, namely: one area is the test area, the area used to recover carbon fiber, the length is 100mm; the second area is the protected area, which is insulated Waterproof to ensure that the area of the test area is consistent during the experiment, the length is 80mm; the third area is the electrical connection region, which is used to connect the stainless steel joints of the circuit to ensure the circuit connectivity, the length is 65mm, in order to A better electrical conductivity is achieved, in which the rear 20mm is a carbon fiber cloth, which is connected to the stainless steel sheet. Therefore, the surface area of the carbon fiber material in the carbon fiber reinforced cement-based composite material soaked in the electrolyte in the above-mentioned recovery device is 100 mm × 30 mm × 2 = 6000 mm ² .

The manufacturing process of the composite material is as close as possible to the construction method in the civil engineering field. After pouring for 1 day, the mold is removed and then placed in the standard curing room for 28 days. After the curing, the composite material was placed under laboratory conditions for 7 days, dried naturally, and then packaged in a protected area. The protection zone consists of five layers, which are Kraft Silicone Rubber - Insulation Tape - Epoxy Sealant - Insulation Tape - Epoxy Sealant. Firstly, apply a uniform layer of Kraft silicone rubber on the surface of the clean and dry composite board test piece protection surface, and dry it under laboratory conditions for 24 hours; then wrap it on the silicone rubber surface with insulating tape; then use the ring. The oxygen sealant was solid-sealed and placed in a laboratory condition for 48 hours to be naturally cured; then it was wrapped with an insulating tape; finally, it was sealed with an epoxy sealant and allowed to cure under laboratory conditions for 48 hours.

Table 1.1 Specific content of carbon fiber reinforced cement-based cementitious materials

Example 2: Recycling experimental system and experimental parameter design

As shown in Figure 1A of the accompanying drawings, the carbon fiber (experimental) recovery system device mainly comprises four parts: a DC power supply, providing a unidirectional working current for the system; a cathode and anode, the recovered sample is connected as an anode to the positive electrode of the power source, and the degraded cement-based colloid is consumed. The stainless steel piece is connected as a cathode to the negative pole of the power source; the electrolyte includes different concentrations of NaCl base solution and catalyst HNO ₃ ; the data log (Datalog) is connected in parallel with the recovered sample and the stainless steel piece to monitor the sample voltage change. The recovered sample was placed in parallel with the stainless steel sheet and the distance was fixed at 50 m.

The experimental design mainly considers parameters including current density, NaCl concentration in solution, catalyst HNO ₃ concentration, and temperature effects. In order to study the effects of various parameters on the recovery and efficiency of carbon fiber more effectively, two series of experiments were designed in this study.

In the first series of experimental designs, (1) two current intensities (20 mA, 40 mA) were considered, based on the surface area of the carbon fiber material immersed in the electrolyte in the above-mentioned recovery device in the carbon fiber reinforced cement-based composite material described in Example 1. The size is 100mm × 30mm × 2 = 6000mm ² , which means that the two current densities (3333.3mA/m ² , 6666.7mA/m ² ); (2) the sodium chloride concentration of the two electrolytes (2%, 3%) (3) Four catalyst nitric acid concentrations (0 g/L, 1 g/L, 3 g/L, and 5 g/L). Thus, 16 kinds of parameter conditions can be obtained. Each test condition includes 3 parallel test pieces. The detailed test piece grouping and experimental parameters are shown in Table 1.

In the second series of experimental design, the first series of the best solutions were selected, and the effect of temperature on carbon fiber performance and recovery efficiency was considered. Therefore, the second series of test parameters include: (1) two current values (20 mA, 40 mA), corresponding to two current densities (3333.3 mA / m2, 6666.7 mA / m2); (2) sodium chloride concentration of an electrolyte (2%); (3) one catalyst nitric acid concentration (3 g/L) and (4) three temperature gradients (40 ° C, 60 ° C and 75 ° C). Six parameters can be obtained, each of which includes three parallel test pieces. The detailed test piece grouping and experimental parameters are shown in Table 2. It is worth noting that in order to achieve recovery at normal temperature and pressure, the maximum temperature set by the experiment is only 75 ° C, and the high temperature conditions are not considered.

The test piece number is determined by the action current intensity, NaCl concentration, HNO ₃ concentration and temperature. For example, the test piece number is “I20S _2.0 H ₃ T ₄₀ ”. The first part “I20” means that the constant current intensity applied by the test piece is 20 mA. two-part "S2" refers to the concentration of the electrolyte is NaCl in deionized water 2% by mass of the third portion "H _3" refers to the concentration of HNO ₃ per liter of the electrolytic solution was added 3g / L. The fourth part "T40" means that the temperature of the electrolyte is kept at 40 °C during the experiment. Without the fourth part, the test is carried out at room temperature (temperature is 25 degrees)

Example 3: Experimental test method

3.1 sample voltage monitoring

The HIOKI-LR8400 data logger (Datalog) manufactured by Nissin Electric Co., Ltd. was used to collect data once per hour. The frequency of the frequency is 1h/time and the power frequency is 50HZ.

3.2 Carbon fiber monofilament tensile performance test

According to the carbon fiber monofilament tensile strength test specification ISO 11566 [54], the carbon fiber monofilament tensile test was carried out using a nano UTM 150 model nano-stretcher manufactured by Agilent, USA; the test system was UTM-Bionix Standard Toecomp Quasistatic. The test parameters were set as follows: application load 750 μN, tensile rate 0.2 μm/s, load resolution 50 nN, displacement resolution <0.1 nm, tensile resolution 35 nm, actuator maximum displacement 1 mm. The test temperature is 20 ° C - 30 ° C, and the air humidity is 40%.

Before the carbon fiber monofilament tensile test, the carbon fiber monofilament should be fixed on the photo paper of 15mm 20mm in size, and the middle of the photo paper is a circular hole with a diameter of 6mm. The carbon fiber monofilament is adhered to the horizontal diameter of the round hole by using the paste glue. On the fiber, the fiber should not be too tight or too loose.

After the sample is prepared, it is placed in laboratory conditions for one day, and the glue is allowed to dry naturally. The sample can be loaded into the nano-tensile fixture, then the edges of the photo paper are cut and the test begins. The carbon fiber monofilament test length is 61 mm, the number of samples to be tested per sample is 20, and the carbon fiber monofilament strength result is 20 sample intensity average. The tensile strength formula of the monofilament is as follows:

Where σ _f — tensile strength of monofilament (MPa)

F _f — monofilament fracture maximum load (N)

D—monofilament diameter (mm)

The diameter of the carbon fiber monofilament was measured using a laser caliper manufactured by Changchun Industrial Optoelectronic Technology Co., Ltd. The sample is placed on the sample holder, and the diffraction dark line spacing of the monofilament is measured by the diffraction principle. The exact diameter of the monofilament can be calculated by formula conversion, and the formula is as follows:

d=kLλ/x _k =Lλ/S (2-2)

Where d-monofilament diameter (nm)

S—dark line diameter (cm)

L—the distance from the sample to the diffraction screen

x _k — the distance from the kth to the optical axis

Parameter setting: L=60cm, λ=532nm

3.3 Carbon fiber monofilament interface shear strength test

The HM410 composite interface feature evaluation device manufactured by Japan Toyon Co., Ltd. was used for the droplet embedding test. The test parameters were set as follows: the test speed was 0.12 mm/min, and the microscope magnification was 2 times.

According to literature studies ^[55] , the diameter of the test resin sphere should be selected from 40 μm to 80 μm. The number of resin balls tested in each sample was 5, and the interfacial shear strength results were averaged. The interface shear strength formula is as follows:

Where F - load value (μN)

D—monofilament diameter (μm)

L—resin ball diameter (μm)

3.4 Environmental Scanning Electron Microscopy (ESEM) Test

The surface morphology of the recovered carbon fiber was observed and analyzed by using the FINA company's Quanta TM 250FEG model scanning electron microscope. Select high vacuum mode, the working distance is about 10mm, and the test acceleration voltage is 20KV. In order to obtain a clearer and more accurate surface topography, it is necessary to increase the conductivity of the carbon fiber, so the sample is subjected to gold spray treatment in an ion sputtering apparatus before being tested.

3.5 atomic force microscope (AFM) test

The ICON-PT-PKG model scanning probe microscope produced by Bruker Company of USA was used to test the recovered carbon fiber to obtain two-dimensional and three-dimensional images of the surface topography and undulation.

Therefore, the sample scanning range of this experiment was 4 μm, and the tapping mode was adopted, and the scanning rate was 1.0 Hz. In order to ensure the success rate of the test, the length of the carbon fiber monofilament should not be less than 20 mm.

The image was analyzed and calculated using NanoScope Analysis 1.8 software. In the four roughness expression formulas of the software, Ra was selected to characterize the roughness. The calculation formula is as follows:

N _x - the number of steps in the X axis

N _{y —} the number of steps in the Y axis

3.6 X-ray analyzer (XRD)

The D8Advance high-resolution X-ray analyzer manufactured by Bruker of Germany was used to scan and recover the recovered carbon fiber, and the crystal structure information of the surface component can be qualitatively obtained. Using Continuous PSD fast mode, the working voltage is 40KV, the working current is 200mA, the test copper target radiation wavelength is 154mm, the scanning angle is 10°~80°, the step size is 0.02°, and the scanning time per step is 0.2S. The phase analysis of the map was performed using Jade 5.0 software.

3.7 X-ray photoelectron spectroscopy (XPS)

The ULVAC-PHI VPII model photoelectron spectrometer was used to perform the full-spectrum scanning of the recovered carbon fiber in the range of 0eV～800eV to obtain the surface element information, and then the C1s were scanned with high resolution, and the results were performed by XPSPeak4.1 software. Gaussian function and Lorentz function fitting, analysis of the type and content of functional groups. When testing, it is necessary to ensure that the carbon fiber is placed flat on the test bench. The X-ray source of the monochromator is an Al target, and the test elements include: C, O, Cl, N, Si, Ca, and 90° is selected as the incident angle.

Example 4: Electrochemical recovery process design

The recycling process step mainly involves three parts: (A) placing the prepared carbon fiber reinforced cement-based composite material (plate) in the electrolyte; (B) energizing the carbon fiber reinforced cement-based composite material placed in the electrolyte, wherein the carbon fiber The reinforced cement-based composite material is connected to the positive electrode of the power source, and the current is controlled within a suitable size range; and (C) the electrification reaction is taken out from the electrolyte for a suitable time (usually 8-240 hours). In the recovery process provided by the present invention, the current magnitude is controlled at 20 mA and 40 mA according to different groupings; the sodium chloride concentration (% by weight) is controlled at 2.0% and 3.0%; the catalyst HNO ₃ concentration is controlled at 0%, 1 %, 3%, and 5%), a total of 16 groups of test samples. Detailed sample grouping and experimental parameters are shown in Table 4.1. The sample number is determined by the current magnitude, NaCl concentration and catalyst HNO ₃ concentration. For example, the sample number is “I20S _2.0 H ₁ ”. The first part “I20” means that the current applied by the sample is 20 mA, and the second part “S _2.0 ” refers to electrolysis. The NaCl concentration in the liquid was 2.0%, and the third portion "H ₁ " means that the concentration of HNO ₃ added per liter of the electrolyte was 1 g. The specific experimental parameters and grouping conditions are shown in Table 5.1. The electrochemical recovery cycle was 8 days. After the recovery, the sample was taken out, the cement-based colloid on the surface was removed, and the obtained carbon fiber was washed and dried, and then subjected to various tests.

Table 4.1 Experimental sample grouping and parameters

Example 5: Cleaning and removing the carbon fiber

The first series of experimental electrochemical recovery cycles was 8 days, and the second series of experimental electrochemical recovery cycles was 4 days. In the recycling process, the cement-based gel has a small amount of dissolution, and there are fine cementitious material particles in the solution and on the cathode of the stainless steel sheet. After the recovery, the test piece was taken out from the liquid, and it was found that the inorganic glue was still connected to the carbon fiber, as shown in FIG. Therefore, the obtained carbon fiber recyclate is a mixture of carbon fiber and cement-based inorganic gum. In other words, the recovered carbon fiber is still joined to the cement-based inorganic glue. However, after the electrochemical recovery reaction, the cement-based gel material becomes very soft and can be easily removed with a hard straight brush or a rigid plate. However, a similar strong rejection may leave a layer of colloid on the surface of the carbon fiber that is difficult to remove. In order to better remove the cement-based gel method, a hole may be inserted every 0.1 mm or more on the surface of the carbon fiber recovery material, and then washed with a water flow of 0.1 MPa or more, and the scouring time is 3 seconds or more to remove the cement-based inorganic material. gum.

Example 6: Performance test of recycled carbon fiber

6.1 Hardness testing of carbon fiber recyclate

After the end of the electrochemical reaction, the resulting carbon fiber recyclate comprises carbon fibers and an inorganic gum, typically in the form of a plate or strip. The hardness of the coated pencil hardness test method was tested.

The QHQ-A pencil hardness tester produced by AIPLI Instrument Co., Ltd. was selected and placed on the surface according to the specification GB/T6739-2006/ISO15184:1998 under the conditions of temperature (23±2) °C and relative humidity (50±5)%. A uniform structure of the plate, the pencil is pressed down on the surface of the composite at a 45° angle under a load of 750g, pushing 10mm away from the operator at a speed of 0.5mm/s to 1mm/s, from the pencil softest level 9B Initially, the cohesive failure visible to the surface of the composite was observed and the depth of failure was measured using a vernier caliper with an accuracy of 0.02 mm. The detailed hardness grade of the tested composites is shown in Table 6.1.

Table 6.1 Composite material hardness and cohesive failure depth

Note: The hard part refers to the part of the sample with hardness ≥ 9H, and the soft part refers to the part with hardness < 9H. The hardness of the pencil hardness tester from low to high is: 9B-8B-7B-6B-5B-4B-3B-2B-1B-HB-FH-2H-3H-4H-5H-6H-7H-8H- 9H

It can be seen from the table that the samples of each group of carbon fiber reinforced cement-based composite materials have a certain degree of softening after electrochemical recovery, and the most significant factor affecting the softening degree is the higher concentration of catalyst HNO ₃ and HNO ₃ . The more severe the degradation of the composite material, the lower the hardness. The hardness of the H ₀ series is divided into two parts, the hardness of the hard part is much larger than 9H, the hardness of the soft part is also 2B, and the area of the soft part is small, indicating that the electrochemical action of the sodium chloride solution alone enhances the carbon fiber. Cement-based composite samples are far from achieving a degree of damage softening and softening unevenness. In the H ₁ series, the samples of I20S _2.0 H ₁ and I40S _2.0 H ₁ are still divided into hard and soft parts. The hardness of the hard part is greater than 9H and 9H, respectively. The hardness of the soft part is 5B and 9B respectively. I20S _3.0 The sample hardness of H ₁ and I40S _3.0 H ₁ was 7B and 9B, respectively. The above results show that the higher the NaCl concentration, the greater the softening of the carbon fiber reinforced cement-based composite sample, and the softer the hardness. Similarly, the carbon fiber reinforced cement-based composite sample is softer due to the increase in current. The hardness of the H ₃ and H ₅ series samples is less than 9B, and the above conclusion can be obtained from the comparison of the depth of cohesive failure caused by the test.

3A to 3D are SEM scan results of the carbon fiber recyclate, wherein FIG. 3A is the interface between the cement-based and carbon fiber of the carbon fiber reinforced cement-based material which has not been electrochemically recovered, and the rib groove The groove structure is quite complete and regular, and it can form a strong mechanical bite with carbon fiber. The interface has only very small holes, and no cracks and other defects are seen. Fig. 3B is a partial enlargement (magnification 10000 times) at the box in Fig. 3A, from which a network structure in which the cement paste and the polymer are interlaced with each other can be found, which increase the strength and bonding property of the material itself. . Fig. 3C shows the interface between the cement-based material and the carbon fiber of the carbon fiber recyclate in I40S _3.0 H ₁ . It can be seen that the rhombic groove structure has been divided into broken small units by the large cracks in the longitudinal and lateral directions, and is in a fluffy shape. At the same time, there are many large crack pores distributed, the porosity is increased sharply, the interface has completely lost the mechanical bite cooperation with carbon fiber, and the adhesion is greatly reduced. Figure D is a partial enlargement (magnification 10,000 times) at the box in Figure C. It can be seen that the inside of the crack is a white loose structure, the intercalated network structure of the cement paste and the polymer has been destroyed, and the cement-based material is hollowed out. The bond between the carbon fiber and the cement-based interface has been lost.

6.2 Carbon fiber recovery

As can be seen from Table 6.2 below, the carbon fiber precursor has a mass of 841 mg, and the carbon fiber cloth with a mass of 30 mm × 100 mm is weighed. It should be noted that the H ₀ series is recovered from the sample of the carbon fiber reinforced cement-based composite material. The obtained carbon fiber recyclate has a large hardness and cannot easily remove the cement-based material without any effort, so it is defined as a carbon fiber recovery amount of 0 g/L, which is not listed in the table. The amount of carbon fiber recovered from different group samples is different, and the amount of carbon fiber recovered between different groups is intuitive, as shown in Figure 4. It can be found that the carbon fiber recovery amount increases first and then decreases with the increase of HNO ₃ concentration, and the carbon fiber recovery amount is the largest when the HNO ₃ concentration is 3g/L. In the H ₁ group (1 g / L), the recovery of I20S _2.0 and I40S _2.0 was significantly lower, only 233 mg and 286 mg, because only the carbon fiber of the soft part was recovered, and the area of the soft part was relatively small in the recovery area. The H ₅ series samples have less carbon fiber recovery, mainly because the carbon fiber is more deteriorated, the surface layer is peeled off, and it becomes very fine and short hair, which adheres to the cement-based material and is also lost during the cleaning stage. The I40 series carbon fiber recovery is generally lower than the I20 series, and the S _3.0 series carbon fiber recovery is lower than the S _2.0 (except when B is 1g/L), indicating that the larger current and larger sodium chloride concentration cause the carbon fiber to deteriorate more. . Not conducive to carbon fiber recycling.

Table 6.2 Carbon fiber recovery under different parameters

Note: 1) DB: indicates that the failure mode is the peeling of the inorganic fat layer.

2) CB: indicates that the failure mode is the interface peeling damage between carbon fiber and inorganic grease

3) EB: indicates that the failure mode is carbon fiber surface peeling damage

In order to determine whether the current plays a role in the softening of carbon fiber reinforced cement-based composite samples, a comparative experiment was conducted to immerse the carbon fiber reinforced cement-based composite samples in the catalyst B (HNO ₃ ) at a dose of 1 g/L and 3 g, respectively. In the 2.0% NaCl solution of /L, 5g/L, 8g/L and 10g/L doses, they were named S _2.0 H ₁ , S _2.0 H ₃ , S _2.0 H ₅ , S _2.0 H ₈ and S _2.0 H ₁₀ , respectively. The time is 8 days.

Carbon fiber reinforced cement-based composites have some differences before and after soaking, the color becomes lighter, and some small holes appear on the surface. In order to judge the treatment effect of catalyst B (HNO ₃ ) more accurately, the hardness test is carried out, and the results are shown in Table 6.3. It can be seen from the table that the hardness of the treated composite is still very high. When the concentration of HNO ₃ reaches 10g/L, the hardness of the composite is 3B. The cement colloid can not be removed without the aid of mechanical tools, and the concentration is high for a long time. When the catalyst B (HNO ₃ ) solution is soaked, the carbon fiber properties are greatly deteriorated. It indicates that current plays an important role in the softening of carbon fiber reinforced cement-based composites, and electrochemical treatment is more effective in conforming with materials.

Table 6.3 Hardness of composite after B electrolyte treatment

6.3 sample voltage detection

As can be seen from Figure 5, the voltages of all samples remained substantially stable during the electrochemical recovery cycle without significant fluctuations. The sample voltages of different groups are different. The H ₀ (0g/L) group has the highest voltage and the highest relative fluctuation. The reason may be that the catalyst HNO ₃ has a slower softening effect on the carbon fiber reinforced cement matrix composite sample and the porosity is very small. The conductivity of the sample is not good, so the voltage is high and the fluctuation is large. The voltage of the H ₅ series sample is lower than the H ₀ series, but it is still relatively high. In the H ₅ series, the damage of the sample cement-based material is very serious and has been applied to the carbon fiber. The higher voltage may be caused by the deterioration of the carbon fiber and the increase in resistance. Big related. The sample voltages of H ₃ (3g/L) and H ₁ (1g/L) groups are lower, which is due to the milder effect of electrochemical action on carbon fiber reinforced cement-based composites, the deterioration of carbon fibers is slight, and the electrical conductivity is better. In general, the I40 series sample voltage is larger than the I20 series, and the S _3.0 series sample voltage is larger than the S _2.0 series, indicating that the larger the voltage and the NaCl concentration, the larger the resistance value, and thus the higher the voltage.

It can be seen from Table 5.5 that the diameter of the recovered carbon fiber does not change, indicating that although the carbon fiber undergoes electrochemical oxidation and acid corrosion during the electrochemical recovery process, there is substantially no peeling of the surface of the carbon fiber. The tensile strength of the monofilament of the carbon fiber precursor was 3588 MPa, and the tensile strength of I20S _2.0 H ₁ in the recovered carbon fiber was 3072 MPa, which was 85.62% of the carbon fiber precursor; the tensile strength of I40S _3.0 H _{5 was} the lowest. 2162MPa, only 60.26% of carbon fiber precursor. The tensile strength of the monofilament of other recycled carbon fibers showed a different degree of decline compared to the carbon fiber precursor, as shown in Figure 6.

As shown in FIG. 6 of the drawings, the recycled carbon fiber resulting single filament tensile strength with increasing concentration of HNO ₃ decreased tensile strength in 0 ~ 3 (g / L) concentration of HNO ₃ in section, of carbon fibers The decrease is small, and the tensile strength of carbon fiber in the range of HNO ₃ concentration of 3 to 5 (g/L) drops sharply, indicating that the higher the concentration of HNO ₃ , the more serious the deterioration of carbon fiber, especially when the concentration of HNO ₃ exceeds 3 (g). /L) After. When the concentration of HNO ₃ is 1 (g/L) and 3 (g/L), the difference in tensile strength between carbon fibers under different parameters is not large, and the tensile strength of H ₁ series carbon fibers is between 2987 MPa and 3072 MPa. _The tensile strength of ₃ series carbon fiber ranges from 2898MPa to 2974MPa. The tensile strength of I20 series carbon fiber is higher than that of I40 series. The tensile strength of S _2.0 series carbon fiber is higher than that of S _3.0 ; when the concentration of HNO ₃ is 5 (g/L) At the same time, the difference in the strength of the carbon fiber between the different parameters is relatively small, but the sample of the small current series is still higher than the sample of the high current series, and the sample of the low sodium chloride concentration is higher than the sample of the high concentration series.

6.4 Interfacial shear properties of recycled carbon fibers

It can be seen from Table 6.4 that the interfacial shear strength of carbon fiber precursor and inorganic grease is 27.09 MPa, the failure mode is DB, and the interfacial shear strength of the recovered carbon fiber is large, except for the H ₅ series, other series of sample shearing The strength is greater than or equal to the carbon fiber precursor, the failure mode is related to the HNO ₃ concentration, the failure mode of the H ₁ series sample is DB, the destruction mode of the H ₃ series sample is CB, and the failure mode of the H ₅ series sample is EB, with the concentration of HNO ₃ The increase in the location of the damage from the inorganic lipid layer to the interface layer to the carbon fiber surface.

Table 6.4 Interfacial shear strength of recycled carbon fiber

Note: 1) DB: indicates that the failure mode is the epoxy layer peeling damage

2) CB: indicates that the failure mode is the peeling failure of the interface between carbon fiber and epoxy resin

3) EB: indicates that the failure mode is carbon fiber surface peeling damage

It can be seen from Fig. 7 that the interfacial shear strength of the recovered carbon fiber decreases with the increase of the HNO ₃ concentration, but the carbon fiber recovered by the H ₁ and H ₃ series is larger than the shear strength of the original yarn, indicating that it is at a lower concentration. Electrochemical oxidation under B conditions can increase the shear strength. As can be seen from Fig. 8A, the carbon fiber precursor has a failure mode of DB, the inorganic lipid layer is peeled off, and the surface of the carbon fiber is bonded with a smooth resin; Figs. 8B and 8C are I20S _2.0 H ₁ and I40S _2.0 H ₁ , respectively. Destroying the image, although the failure mode is still DB, the resin layer bonded on the surface of the carbon fiber is rough and uneven, especially the I20S _2.0 H ₁ sample, indicating that the carbon fiber of the H ₁ series is more strongly bonded to the inorganic grease, probably due to At low concentrations of B, the microstructure of the carbon fiber surface is oxidized and etched better, and the mechanical bite is stronger; in Figures 8D and 8E, the failure modes of I20S _2.0 H ₃ and I40S _2.0 H ₃ are CB, but After peeling and ruining, the surface of the carbon fiber is bonded with a needle-like slender inorganic grease. The acicular resin not only increases the surface area of the fracture, but also acts like a steel rib, greatly improves the mechanical bite force and increases the adhesion to the inorganic grease. Knot performance, so the shear strength of the S _2.0 series samples is still higher than that of carbon fiber strands. When the concentration of HNO ₃ is 1 (g/L) and 3 (g/L), the shear strength of I20 series samples is higher than that of I40 series, I20S _3.0 H ₁ ; the shear strength of S _2.0 series samples is higher than that of S _3.0 series; In the H ₅ series, the shear strength of the sample with small current and low B concentration is greater, but due to excessive oxidation etching, the influence of current and B parameters on shear strength is very small. See Figure 8F and Figure 8G for I20S. The peeling mode of _2.0 H ₅ is CB, there is no resin residue on the surface of carbon fiber, and the longitudinal groove structure of the surface is seen, indicating that the bonding performance of carbon fiber and inorganic grease is degraded; the failure mode of I40S _2.0 H ₅ is EB, it can be seen that carbon fiber The surface is peeled off a small portion of the skin, which may have been oxidized into a fragile sheet, which is no longer a solid whole with the carbon fiber body; indicating that the recovered carbon fiber is subjected to more severe oxidation when the HNO ₃ concentration is 5%. Corrosion reduces the bonding properties of carbon fiber surface.

Example 7: Detection of recovered carbon fiber

7.1 SEM scan

It has been found that the difference in the microscopic morphology of the carbon fibers recovered from the S _2.0 series and the S _3.0 series is very small, so only the SEM images of the carbon fibers recovered in the S _2.0 series are listed here. As can be seen from Fig. 9A, the surface of the carbon fiber precursor was very smooth and flat, and no defects such as crack crack pits were observed. A small amount of gel particles adhere to the surface of the recovered carbon fiber, which is a residue caused by insufficient cleaning. It can be seen from Fig. 9B and Fig. 9C that the surface of the carbon fiber recovered by I20S _2.0 H ₁ and I40S _2.0 H ₁ has no defects such as crack cracks and pits, except for the adhesion of a very small amount of cement gel. Under the condition of B at a concentration of 1 (g/L), the electrochemical recovery process does not cause serious oxidative degradation on the recovered carbon fibers, so the tensile strength of the carbon fibers recovered in this series does not decrease much. It is found from Fig. 9D and Fig. 9E that the surface of the carbon fiber recovered by I20S _2.0 H ₃ and I40S _2.0 H ₃ is very clean, and little cement gel particles remain, but transverse cracks are found on the surface of individual carbon fibers, forming at the cracks. The weak layer causes the tensile strength of the carbon fiber to decrease, so the tensile strength of the carbon fiber recovered by the H ₃ series is lower than that of the H ₁ series. It is shown that under the condition of Catalyst B at a concentration of 3 g/L, the degree of oxidative degradation of the carbon fiber during the recovery process is increased. As seen from Fig. 9F and Fig. 9G, the surface of the carbon fiber recovered by I20S _2.0 H ₅ and I40S _2.0 H ₅ has more cement gel particles, and longitudinal cracks and transverse cracks are found on the surface of the carbon fiber, and the depth is not shallow, which is reduced. The tensile strength of the carbon fiber recovered by the H ₅ series is seriously reduced, and only the strength of the carbon fiber precursor is 60.26% to 66.64%. It is indicated that under the condition of Catalyst B at a concentration of 5 g/L, the carbon fiber is subjected to severe oxidative degradation during the recovery process. Comparing the carbon fiber images recovered from the I20 series and the I40 series in Fig. 10, it was found that the carbon fibers recovered by the I40 series had more surface defects, indicating that the large current action caused the damage of the recovered carbon fibers to be more serious.

7.2 AFM scan

The surface topography of carbon fiber plays a very important role in the interfacial adhesion properties. It is characterized by roughness and morphology structure. The AFM scanning test results of carbon fiber precursor and recovered carbon fiber are shown in Table 7.1 and Figure 10, respectively. It should be noted that the recycled carbon fibers of the S _2.0 series and the S _3.0 series have little difference in roughness and morphology, so only the carbon fiber AFM images recovered by the S _2.0 series are listed here.

Table 7.1 Roughness of recovered carbon fiber

As can be seen from Fig. 10A and Fig. 10B, the surface of the carbon fiber precursor is very smooth, has no longitudinal groove structure, has almost no skin convex structure, and has a calculated roughness of 144 nm. From Fig. 10C to Fig. 10F, it can be found that in the H ₁ carbon fiber series, due to the oxidative etching action of the recycling process, a significant longitudinal groove structure and a skin convex structure appear on the surface of the carbon fiber, and these fine structures function like steel ribs. Greatly improve the mechanical bite of carbon fiber and inorganic grease, increase the surface roughness of carbon fiber, the roughness of I20S _2.0 H ₁ and I40S _2.0 H ₁ are 180nm and 178nm respectively, increase the specific surface area, improve the wettability and improve the interface. Bonding properties, therefore, the shear strength of the carbon fiber recovered from the H ₁ series is much higher than that of the carbon fiber precursor. It can be seen from Fig. 10G to Fig. 10J that when the concentration of HNO ₃ is increased to 3, the surface of the carbon fiber still has a longitudinal groove structure, but is weaker than the H ₁ series, and the convex structure on the surface of the I20S _2.0 H ₃ carbon fiber is increased, and the I40S _2.0 is increased. H ₃ has only different longitudinal groove structures, and the calculated roughness is 208 nm and 162 nm, respectively. The longitudinal groove structure becomes weak, resulting in a decrease in the mechanical bite of the carbon fiber surface. Therefore, the shear strength of the carbon fiber interface recovered by the H ₃ series is obtained. It is lower than the H ₁ series, but still higher than the carbon fiber precursor, indicating that the concentration of HNO ₃ is increased, causing the carbon fiber to undergo oxidative etching and the like to be deteriorated, resulting in weakened interface shear strength. It can be seen from Fig. 10K to Fig. 10N that when the HNO ₃ concentration continues to increase to 5, the longitudinal groove structure is hardly visible on the surface of the I20S _2.0 H ₅ and I40S _2.0 H ₅ carbon fibers, and only the miscellaneous convex structure is obtained, and the calculated roughness is obtained. The degrees are 104 nm and 121 nm, respectively. It should be noted that the longitudinal grooves of the I40S _2.0 H ₅ are produced during production, not by oxidative etching. Excessive oxidative etching causes the activated carbon particles to fall off, and the longitudinal groove structure cannot be formed. The mechanical bite force of the carbon fiber drops sharply, resulting in a decrease in the shear strength of the carbon fiber recovered by the H ₅ series, slightly lower than that of the carbon fiber precursor, and severely oxidized. The adhesion between the convex mechanism and the carbon fiber body is weakened, and peeling is likely to occur when the resin droplets are dialed out, resulting in an EB failure mode. The above shows that when the concentration of HNO ₃ is low, the small amount of oxidative etching in the electrochemical recovery process increases the interfacial shear strength of the carbon fiber, and when the concentration of HNO ₃ increases to a certain extent, the excessive oxidation etching causes the carbon fiber to The interface shear strength is reduced.

7.3 XPS scanning

After detection, the XPS scanning full spectrum and the C1s high resolution narrow spectrum of the recovered carbon fiber are shown in Fig. 11A to Fig. 11H, and the left column is the scanning full spectrum of the sample. It can be seen from the scanning full spectrum that there are five main peaks in the figure, namely two main peaks: C (284.6 eV) and O (532.0 eV); three secondary peaks: Si (99.5 eV), Cl (199.8 eV). ) and Ca (347eV). The basic elements of the carbon fiber precursor are carbon and oxygen, and the small amount of silicon, chlorine and calcium detected is introduced during the experiment. The specific chemical element content of the carbon fiber surface recovered from the VCF and I20S _2.0 groups is shown in Table 7.2.

Table 7.2 Surface Element Content of Carbon Fiber Recovered by VCF and I20S _2.0 Group (%)

It can be seen from the table that the carbon fiber surface has a carbon content of 79.3% and an oxygen content of 20.7%, and no other element content is detected. The carbon content of all recovered carbon fiber surfaces is relatively close, which is about 10% lower than that of carbon fiber precursors, and the oxygen content is increased to some extent. From the oxygen-carbon ratio, the recovered carbon fibers are much higher than the carbon fiber precursors. 0.2610, in the three HNO ₃ concentration gradients, H _{3 has} the highest oxygen-to-carbon ratio, followed by H ₅ , and the lowest is H ₁ , indicating that H ₃ is the optimal concentration in the region and can introduce more oxygen to obtain a larger Surface activity enhances the chemical bonding ability with inorganic lipids. From the perspective of chlorine content, an increase in the concentration of HNO ₃ increases the chlorine content of the carbon fiber surface. A certain amount of calcium is introduced on the surface of all carbon fiber samples, which may be the residue of the cement-based material on the surface of the carbon fiber. In addition, the I20S _2.0 H ₁ carbon fiber surface monitored a 3.4% silicon content. Using the software XPSPeak4.1, the C1s high-resolution narrow spectrum is divided into the following six chemical bond peaks according to the binding energy: Gauss Lorenz fitting: graphite state C~C (284.4eV), amorphous C~C (284.8eV) C=O (285.5 eV), C~O (286.2 eV), C-Cl (287.2), and O-C=O (288.4 eV). The C1s peak fitting is shown in the right column of Figure 5.15. It should be noted that the C1s of the carbon fiber precursor is double-peak and there is no area after the 288eV peak, so the fitting results show that the surface of the carbon fiber precursor does not contain O. ~C=O bond, the other carbon-carbon and carbon oxidation bond peaks are offset, indicating that the carbon fiber precursor surface activity is not good. The content of the C-Cl bond on the surface of the recovered carbon fiber is zero, indicating that the chlorine on the surface of the recovered carbon fiber exists in an adsorbed state, and is not chemically bonded. The specific recovered carbon fiber surface functional group content is shown in Table 7.3.

Table 7.3 Carbon fiber surface functional group content (%) recovered from VCF and I20S _2.0 groups

It is found from the table that the total amount of graphite and amorphous C-C bonds on the surface of carbon fiber precursor is 51.1%, and the carbon-carbon bond content of I20S _2.0 H ₁ is slightly increased to 52.8%, I20S _2.0 H ₃ and I20S _2.0 H ₅ decreased, 49.4% and 48.4% respectively. In terms of carbon-oxygen bonds, carbon fiber obtained recycled C ~ O bond of a major decline, decrease of the amount of descending _{_{order: H 3> H 5> H}} 1; recovered carbon fibers C = O bond appeared small The decrease in the amplitude is zero in the content of the strongly hydrophilic functional group O to C=O, compared to the content of the carbon fiber precursor, and the recovered carbon fiber is high in content, and H ₃ >H ₅ >H ₁ . The above situation indicates that the carbon fiber undergoes a certain degree of oxidation during the recovery process, the surface oxygen content increases, the surface activity is increased, and the O~C=O bond appears, which greatly improves the chemical bonding ability of the carbon fiber and the inorganic grease; The oxygen-carbon ratio and functional group content of the recovered carbon fiber showed that the degree of oxidation of carbon fiber was too low when the concentration of HNO ₃ was 1.0 g/L. When the concentration of HNO ₃ was 3.0 g/L, the degree of oxidation of carbon fiber was the best, and HNO was increased. _The concentration of ₃ only increases the C=O bond on the surface of the carbon fiber.

7.4 XRD

Referring to Figures 18A and 18B of the accompanying drawings, the XRD patterns of the carbon fibers recovered by the I20 series and the I40 series at different temperature gradients are mainly shown, wherein the XRD spectrum of all recovered carbon fibers has only one strong diffraction peak and the peak position is at 2? Near =26°, after phase retrieval, it was judged as C, indicating that other crystal structure compounds were not introduced into the surface of the carbon fiber during the electrochemical recovery process.

It is worth mentioning that, from the figure, it can be further observed that the XRD spectrum is basically higher in temperature, the higher the diffraction intensity of the characteristic peak, the sharper the peak, indicating that the higher the recovery temperature, the better the crystallinity of carbon fiber and the smaller the crystal grain. . Papirer E's research shows that the smaller the surface of carbon fiber, the more unsaturated C atoms on the surface edges and edges, the higher the surface activity, which can improve the bonding performance of carbon fiber and resin to some extent, and improve the pulling of carbon fiber. Stretch strength. The I20 series carbon fiber has better characteristic peak than the I40 series, indicating that the small current effect has less influence on the graphite block structure of the carbon fiber, and is more conducive to recovering the mechanical properties of the carbon fiber.

Example 8: Effect of temperature on electrochemically recovered carbon fiber

Similar to other chemical reactions, the chemical reaction process for the recovery of carbon fibers by electrochemical methods should also have suitable reaction conditions. The present invention determines the appropriate temperature for the electrochemical recovery process of the present invention by the following experimental results. Similarly, multiple sets of samples (shown in Table 6.1 below) were used to test the appropriate reaction temperatures, with current intensities of 20 mA and 40 mA, NaCl concentration of 2.0 (%), and HNO ₃ dose of 3.0 g/L. The temperature gradient is a total of 6 sets of four temperature gradients that exclude extreme temperatures of extremely low yields (very low, such as below 0 ° C, and temperatures above 100 ° C). The sample number is determined by the action current, NaCl concentration, catalyst HNO ₃ concentration and temperature gradient, such as the sample number “I20S _2.0 H ₃ T ₄₀ ”. The first part “I20” means the current applied by the sample is 20 mA, the second part “S _2.0 "refers to the electrolyte concentration of 2.0% NaCl, part III" H ₃ "means that the catalyst is added to the electrolyte concentration of HNO ₃ is 3.0g / L. The fourth part "T ₄₀ " means that the temperature of the electrolyte is maintained at 40 ° C during the experiment. Detailed experimental groupings and experimental parameters are shown in Table 8.1.

Table 8.1 Experimental sample grouping and parameters

The electrochemical recovery period of this part was 4 days. After the recovery, the composite was tested for hardness. The cement-based colloid of the composite is then removed and the carbon fibers are removed. The recovered carbon fiber obtained is washed and dried, and various tests are performed. After testing, the recovered carbon fiber still maintains a tow shape with a length of about 100 mm, which is basically the same as the sample recovery length, and the surface is lustrous, indicating that the carbon fiber is less damaged by oxidation and corrosion during the recovery process.

8.1 Carbon fiber reinforced cement-based composite samples and carbon fiber recovery

It can be seen from Table 8.2 that after 4 days of recovery cycle, the carbon fiber reinforced cement-based composite samples have a very large hardness drop, which is far less than the 9B hardness grade. The cohesive failure depth of the I20S _2.0 H ₃ T ₇₅ sample reaches 1.88 mm. Close to the carbon fiber layer, indicating that the temperature has a great influence on the softening of the carbon fiber reinforced cement-based composite material, and compensates for the short recovery cycle. At the same time, it can be found from the depth of cohesive failure of the composite material that the higher the temperature, the more severe the softening degree of the composite material.

Table 8.2 Composite material hardness and cohesive failure depth

Note: The hardness of the pencil hardness tester from low to high is: 9B to 8B to 7B to 6B to 5B to 4B to 3B to 2B to 1B to HB to F to H to 2H to 3H to 4H to 5H to 6H to 7H～8H～9H

As seen from Table 8.3 and Figure 12, the recovery of carbon fiber showed a high first and then low trend with increasing temperature. At the temperature of T ₄₀ (40 ° C), the carbon fiber recovery was the largest, and the recovery of I20S _2.0 H ₃ T ₄₀ was 772 mg. , reaching 91.8% of the carbon fiber precursor. Although the recovery cycle at high temperature is only half of the normal temperature (T ₀ , 25 ° C), the recovery of carbon fiber is higher. The reason is that the shorter the electrochemical oxidation time of the carbon fiber, the lower the degree of deterioration, and the more the resulting filament Less, so the amount recovered is more. The carbon fiber recovery of I20 series samples is obviously higher than that of I40 series, especially in the high temperature stage. In the process of carbon fiber extraction and cleaning, I40 series carbon fiber has more filaments, not only more cemented on cement-based gel, but also a part of The water flow washed away, indicating that the deterioration of the carbon fiber caused by the large current is more serious.

Table 8.3 Carbon fiber related properties under different temperature gradient conditions

8.2 Sample voltage detection

It can be seen from Fig. 13 that the sample voltage of each group is low, and the sample voltage difference value of different parameter conditions is small, indicating that the system resistance of the sample is very small under high temperature conditions. The voltage of all samples remained stable during the electrochemical recovery cycle. The I20 series sample voltage fluctuated within 0.15V, and the I40 series sample voltage fluctuated within 0.1V. The sample voltages of the same temperature conditions are close, and the voltage of the T ₂ series samples is the lowest, indicating that the conductivity is very good under these conditions, and the degree of deterioration of carbon fibers is very low.

8.3 Recovered carbon fiber monofilament tensile strength test

It is found from Table 8.4 that the carbon fiber diameter remains unchanged at 7 μm, indicating that the electrochemical oxidation and acid corrosion of the carbon fiber during the electrochemical recovery process are less severe, and there is substantially no peeling of the surface of the carbon fiber. Among the recovered carbon fibers, the tensile strength of I20S _2.0 H ₃ T ₃ is up to 3,214 MPa, which is 89.58% of the carbon fiber precursor; the tensile strength of I40S _2.0 H ₃ T ₁ is 2,881 MPa, which is 80.30 of the carbon fiber precursor. %. The tensile strength of the monofilament of other recycled carbon fibers is lower than that of the carbon fiber precursor. The relationship between the tensile strength of the monofilament and the temperature gradient is shown in Fig. 14.

Table 8.4 Tensile strength of recycled carbon fiber under different temperature gradient conditions (ISO11566)

As is apparent from Fig. 14, the tensile strength of the monofilament of the recovered carbon fiber showed a tendency to decrease first and then to rise slowly with an increase in temperature. It should be pointed out that under normal temperature T ₀ (25 ° C), the recovery period of carbon fiber is 8 days. Under high temperature conditions, the recovery period is shortened to 4 days, and the carbon fiber is weakened by oxidation and corrosion, so the damage is relatively small. The tensile strength of carbon fiber is naturally higher. However, at a temperature of T ₁ (40 ° C), the tensile strength of the carbon fiber is lower than that at T ₀ , and the carbon fiber should be subjected to some type of more serious deterioration damage at this temperature. The tensile strength of the I20 series sample is higher than that of the I40 series, and as the temperature increases, the difference between the two increases continuously. It may be that under high temperature conditions, the large current makes the oxidation reaction rate of the sample faster.

8.4 Analysis of Interfacial Shear Properties of Carbon Fibers Recovered

It can be seen from Table 8.5 that the destruction mode of the recovered carbon fiber except for I40S _2.0 H ₃ T ₂ is CB, and the failure modes of other samples are all DB. The interfacial shear strength of I20S _2.0 H ₃ T ₂ is up to 28.45 MPa, which is 105.02% of the carbon fiber precursor. The interfacial shear strength of other samples is different compared with the carbon fiber precursor.

Table 8.5 Interfacial shear strength of recycled carbon fiber under different temperature gradient conditions

Note: 1) DB: indicates that the failure mode is the epoxy layer peeling damage

It is found from Fig. 15 that the interfacial shear strength of the recovered carbon fiber increases first and then increases and then decreases with the increase of temperature. The high shear strength of the high temperature sample is higher than that of the normal temperature T ₀ sample. The reason may be that the recovery period of the high temperature sample is only Half of the sample at room temperature is related to the low degree of fine structure of the surface which is oxidized and etched, and the roughness is low. It can be seen from Fig. 16A and Fig. 16B that the fracture interface of I20S _2.0 H ₃ T ₁ and I40S _2.0 H ₃ T ₁ is a smooth inorganic lipid layer with low shear strength of 22.78 MPa and 23.51 MPa, respectively. 84.09% and 86.78% of the silk. As seen from Fig. 16C and Fig. 16D, the failure modes of I20S _2.0 H ₃ T ₂ and I40S _2.0 H ₃ T ₂ are DB and CB, respectively, and the rupture interface is bonded with a lot of acicular elongated inorganic grease, and these acicular resins can The damaged surface area is increased, which acts like a steel crescent rib, which greatly improves the mechanical bite force, so the shear strength of the sample is improved, reaching 105.02% and 98.74% of the carbon fiber precursor, respectively. In Fig. 16E and Fig. 16F, the failure modes of I20S _2.0 H ₃ T ₃ and I40S _2.0 H ₃ T ₃ are both DB, the inorganic lipid layer is destroyed, and a small amount of acicular inorganic lipid can be observed at the destruction interface. The strength is higher, which is 92.69% and 89.66% of the carbon fiber precursor, respectively.

8.5 SEM scan detection

It can be seen from Fig. 17 that the recovered carbon fiber is very clean, the surface of the carbon fiber is not attached with cement gel particles, and no crack cracks and pits are found on the surface of the carbon fiber. Compared with the same parameter sample, there is a crack crack on the surface under normal temperature T ₀ condition. It indicates that the recovered carbon fiber is slightly less affected by oxidation and acid corrosion, and shortening the recovery cycle can effectively reduce the deterioration of the carbon fiber, so that the carbon fiber recovered under high temperature conditions has higher tensile strength.

8.6 AFM scan detection

Table 8.6 Roughness of recovered carbon fiber

The AFM test results of the recovered carbon fibers are shown in Table 8.6 and Figure 18, respectively. FIG carbon fiber series T ₁ is recovered 18A to 18D, the etching degree of oxidation less recovery process, the longitudinal grooves of the surface structure of the carbon fiber shallow, raised structures size between about 20μm ~ 50μm, I20S _2.0 H ₃ The roughness calculated by T ₁ and I40S _2.0 H ₃ T ₁ is 134 nm and 149 nm, respectively, which is not much different from the roughness of 144 nm of the carbon fiber precursor. Therefore, the interfacial shear strength of the recovered carbon fiber is not high. When the temperature continues to rise, Figure 18E to Figure 18H, the surface of the I40 carbon fiber series has a deeper longitudinal groove structure with a larger width. The surface of the I40S _2.0 H ₃ T ₂ is densely convex. The size of these raised structures is about 100 nm~ between 300nm, I20S _2.0 H ₃ T ₂ and I40S _2.0 H ₃ T ₂ roughness 168nm and 169nm, respectively, longitudinal grooves and projections carbon fiber structure to improve the mechanical bite force, the specific surface area to improve wettability, and therefore T The shear failure interface of the ₂ series carbon fiber can bond the needle-like resin, which greatly improves the interfacial shear strength of the carbon fiber. When the temperature rises to T ₃ , as seen from Fig. 18I to Fig. 18L, large-sized expanded protrusions appear on the surface of the carbon fiber, and discontinuous groove structures, I20S _2.0 H ₃ T ₃ and I40S _2.0 H ₃ T ₃ The roughness is 184 nm and 192 nm, respectively. These structures increase the specific surface area and increase the van der Waals force of the infiltrated adsorption resin. However, the roughness excessively reduces the bonding ability of the carbon fiber to the resin, and the structure is disadvantageous for mechanical biting. The interface shear strength is not too high.

8.7 XPS scan detection

After scanning, the scanned full spectrum of the recovered carbon fiber and the high resolution narrow spectrum of C1s are shown in Fig. 19A to Fig. 19F. The left column is the full spectrum of the sample, and the right column is the corresponding high resolution narrow spectrum of C1s and its peak resolution. Figure. It can be seen from the scanning full spectrum that there are six main peaks in the figure, namely two main peaks: C (284.6 eV) and O (532.0 eV); four secondary peaks: Si (99.5 eV), Cl (199.8 eV). ), Ca (347 eV) and N (399.5 eV). The basic elements of the carbon fiber precursor are carbon and oxygen, and the small amount of silicon, chlorine, calcium and calcium detected is introduced during the experiment. See Table 8.7 for the chemical element content of the carbon fiber obtained by the recovery of different temperature gradients.

Table 8.7 Surface Element Content of Carbon Fiber Recovered (%)

It can be seen from the table that the recycled carbon fiber has a certain decrease in the content of C element compared with the carbon fiber precursor, and the oxygen content increases significantly. From the oxygen to carbon ratio, the carbon fiber precursor is only 0.2610. The lowest oxygen-to-carbon ratio of I20S _2.0 H ₃ T ₃ also reached 0.4066, which is more than 1.5 times that of the carbon fiber precursor. This indicates that more carbon is introduced into the surface of the recovered carbon fiber, and more activity is obtained. Among the three temperature gradient samples, the oxygen-to-carbon ratio of I20S _2.0 H ₃ T ₂ is 0.4281, I20S _2.0 H ₃ T _{1 is} slightly lower, the oxygen-carbon ratio is 0.4252, and I20S _2.0 H ₃ T ₃ is the lowest. From the above experiment It is known that the oxygen-carbon ratio of I20S _2.0 H ₃ T ₀ is 0.3859, which indicates that although the recovery period shortens and the oxidation time of carbon fiber becomes shorter, the high-temperature condition causes the oxygen introduction amount on the surface of carbon fiber to be larger. At the temperature of T ₂ , the surface oxygen of carbon fiber The carbon ratio is the largest and then begins to decline. During the recovery process, chlorine is introduced into the surface of the carbon fiber, and the chlorine content decreases as the temperature increases. Further, I20S _2.0 H ₃ T ₂ and I20S _2.0 H _₃ T ₃ surface of carbon fibers also introduces a small amount of nitrogen, silicon, and calcium.

According to the literature and the research that has been carried out, using the software XPSPeak4.1, the high resolution narrow spectrum of C1s is divided into the following six chemical bond peaks according to the binding energy: Gauss Lorenz fitting: Graphite state C～C (284.4eV), non Crystalline C to C (284.8 eV), C=O (285.5 eV), C to O (286.2 eV), C to Cl (287.2), and O to C=O (288.4 eV). The C1s peak fitting is shown in the right column of Figure 6.9. The specific recovered carbon fiber surface functional group content is shown in Table 8.8.

Table 8.8 Recovered carbon fiber surface functional group content (%)

It can be seen from the table that the total amount of graphite and amorphous C-C bonds on the surface of the carbon fiber precursor is 51.1%, and the decrease of I20S _2.0 H ₃ T ₁ and I20S _2.0 H ₃ T ₂ is 44.9%. The I20S _2.0 H ₃ T ₃ increased slightly to 51.4%. Due to the electrochemical oxidation of the recovery process, the C~O bond of the recovered carbon fiber decreased greatly. In the C=O bond, I20S _2.0 H ₃ T ₁ content decreased, I20S _2.0 H ₃ T ₂ and I20S _2.0 H ₃ T ₃ content increased slightly; in the strong hydrophilic group O ~ C = O bond, the lower the temperature, the higher the recovered carbon fiber content, This is probably because the O~C=O bond is more likely to generate carbon dioxide and water at high temperatures ^[34] . The above indicates that the lower the reaction temperature of the recovered carbon fiber, the higher the surface oxidation degree, and the more chemical bonding ability with inorganic grease. Strong, however, because the C~Cl bond content on the surface of I20S _2.0 H ₃ T ₁ is as high as 8.2%, it indicates that the carbon fiber is subjected to more serious chlorination, resulting in a decrease in tensile strength and interfacial shear strength, and the corresponding I20S _2.0 H ₃ chloro and T ₂ I20S _2.0 H _₃ T ₃ is not chemically bonded to the surface, adsorbed form but in It exists.

8.8 XRD analysis

It can be seen from Fig. 20A and Fig. 20B that the XRD spectrum of the recovered carbon fiber has only one strong diffraction peak, and the peak position is near 2θ=26°. After the phase retrieval, it is judged as C, indicating that the surface of the carbon fiber is not in the electrochemical recovery process. Other crystal structure compounds are introduced.

Further, as is clear from the figure, the crystallinity of the recovered carbon fibers is relatively poor. The diffraction peak intensity of H ₁ series recycled carbon fiber is low. When the concentration of nitric acid increases to 3g/L, the intensity of the diffraction peak increases, and the peak becomes sharper. When the concentration of nitric acid continues to increase to 5g/L, the diffraction peak The strength of the peak decreases, and the peak end becomes smooth, indicating that the crystallinity of the carbon fiber of the H ₃ series is relatively good, and the concentration of nitric acid which is too high or too low causes the graphite block structure of the carbon fiber to be greatly affected in the recovery process.

It is worth mentioning that in the above experiments in which the power is continuously recovered, the electrolyzer used may be various electrolytic cells, electrolytic cells, and the like which are well known in the art.

The above electrolysis device as a recovery container is provided with a chemical solution in which a pre-designed recyclant and a catalyst are mixed, which can effectively invade the cement-based cementing material of the carbon fiber reinforced cement-based composite material to be recovered, and destroy the chemical bond thereof. Promote the decomposition of cement-based cementitious materials. The chemical solution includes, but is not limited to, water, HNO ₃ (nitric acid), liquid ethanol, liquid ethylene glycol, various acidic solutions (including but not limited to H ₂ Si ₃ (metasilicate), HCN (hydrocyanic acid). ), H ₂ C ₃ (carbonic acid), HF (hydrofluoric acid), C ₃ COOH (also known as C ₂ H ₄ O ₂ acetic acid, also known as acetic acid), H ₂ S (hydrogen sulfuric acid), HClO (hypochlorous acid) , HNO ₂ (nitrous acid), all organic acids, H ₂ S ₃ (sulfurous acid), etc., various alkaline solutions (including but not limited to potassium hydroxide solution, sodium hydroxide solution, etc.), various Chloride solution (including but not limited to sodium chloride solution, zinc chloride solution, etc.). The above chemical liquid is characterized by being a mixed solution of the above various solutions, and the concentration of each solution is 0.001% to 99.9%,

According to this preferred embodiment of the invention, the carbon fiber material in the carbon fiber reinforced cementitious composite material to be recovered is connected to the positive electrode of the power source in a well-known manner during the energization process to ensure stable operation of the circuit during the recovery process. The method of joining the fiber material to the positive electrode of the power source includes, but is not limited to, dissolving the resin, grinding away the resin, etc., to expose the inner fiber material to facilitate circuit connection.

In accordance with this preferred embodiment of the invention, the cathode material during energization is a well known conductive material including, but not limited to, steel, iron, various metals, various forms of graphite materials.

During the electrification process, the current density is characterized by cooperating with the chemical solution to promote the solution of the cement-based cementitious material in the carbon fiber reinforced cement-based composite material to be recovered, without affecting each of the recovered carbon fibers. Mechanical properties, electrical conductivity, adhesion to organic (epoxy) and inorganic (cement based) cementitious materials and reworkability. The magnitude of the current density is calculated according to the surface area of the carbon fiber reinforced inorganic (cement-based) composite material in which the carbon fiber material is immersed in the electrolyte, and ranges from 3333.3 to 6666.7 mA/m ² .

During the electrification process, the energization time is characterized in that, in combination with the above chemical solution and current, the cement-based cementitious material in the carbon fiber reinforced cement-based composite material to be recovered can be decomposed without affecting the recycled carbon fiber. Various mechanical properties, electrical conductivity, adhesion to organic (epoxy) and inorganic (cement based) cementitious materials and reworkability. The energization time is from 0.5 to 200 hours, preferably from 2 to 120 hours, more preferably from 4 to 48 hours.

During the energization process, various resin aging methods well known in the art can be used to speed up the recovery, such as ultraviolet ray strengthening, ultrasonic strengthening, and microwave strengthening.

In the method for recovering carbon fibers from the carbon fiber reinforced cement-based composite material, the reaction temperature is from 25 ° C to 75 ° C, preferably from 40 ° C to 75 ° C, more preferably from 60 ° C to 75 ° C.

The pressure in the recovery container is adjusted to a preset size, which, together with the above chemical solution, current and temperature, causes expansion and decomposition of the cement-based cementitious material in the carbon fiber reinforced cement-based composite material to be recovered. At the same time, it does not affect the various mechanical properties, electrical conductivity, adhesion to resin materials and reworkability of recycled carbon fibers. The pressure ranges from 0.5 to 20 atm and the pressurization time is from 0.5 to 200 hours.

In the electrochemical recovery method, the distance between the anode and the cathode material has an effect on the recovery effect, the recovery rate, and the recovery cost, and is preferably from 1 mm to 1000 mm, and more preferably from 20 mm to 60 mm.

Further, in the electrochemical recovery method, the carbon fiber is taken out and stored, and then it can be put into production. The method of removal is a variety of well known methods including, but not limited to, ultrasound, drying, heating, and the like, as well as combinations of various methods.

The length of the recovered carbon fiber is an important factor in its reuse value. The carbon fiber recovered is straightened, and the length of the carbon fiber is about 80 mm to 100 mm. The length of the sample recovery part of the experimental design is 100 mm. Considering the length loss of the carbon fiber obtained by the shear recovery, It is known that there is substantially no loss in the length of the carbon fiber during the electrochemical recovery process, indicating that the damage caused by the electrochemical oxidation of the carbon fiber is very slight throughout the recovery process.

According to the preferred embodiment of the present invention, in the method for recovering carbon fibers from a carbon fiber reinforced cement-based composite material, the electrolyte solution contains 1 g/L to 5 g/L of catalyst B, wherein the catalyst B is a soluble acid, which may be But not limited to HNO ₃ . As shown in Figure 4 and Figure 6 of the drawings, the amount of carbon fiber recovered from different carbon fiber reinforced cement-based composite samples is different, and the amount of carbon fiber recovered increases first and then decreases with the increase of HNO ₃ concentration. HNO ₃ At a concentration of 3 g/L, the amount of carbon fiber recovered is the largest. In the HNO ₃ concentration of 1g / L group, the carbon fiber recovery amount was significantly reduced, and the tensile strength of the recovered carbon fiber filaments decreased with the increase of HNO ₃ concentration, and the HNO at 0-3 (g/L) _{In the} concentration range of ₃ , the tensile strength of carbon fiber decreased slightly, and the tensile strength of the recovered carbon fiber decreased sharply in the range of HNO ₃ concentration of 3 to 5 (g/L). Therefore, the concentration of HNO ₃ is preferably controlled at 1 to 3 (g/L), and more preferably controlled at 3 g/L, whereby an ideal recovery effect can be obtained.

Those skilled in the art will appreciate that the embodiments of the invention, which are illustrated in the figures and described above, are merely illustrative and not limiting.

It can thus be seen that the object of the invention can be fully and efficiently accomplished. The embodiment has been described and described in detail to explain the principles of the present invention and the invention is not to be construed as limited. Accordingly, the present invention includes all modifications that come within the scope and spirit of the appended claims.

Claims

A method for recovering high performance carbon fibers from an inorganic cementitious material, comprising the steps of:

(A) placing a carbon fiber-reinforced inorganic composite material in an electrolyte, wherein the electrolyte contains 0.5% to 3% by weight of NaCl and 1.0 g/L to 5 g/L of the catalyst;

(B) energizing the carbon fiber reinforced inorganic composite material placed in the electrolyte, wherein the carbon fiber reinforced inorganic composite material is connected to the positive electrode of the power source, and the current density is controlled to be 3333.3 to 6666.7 mA/m 2 ;

(C) After the energization reaction was carried out for 0.5 to 200 hours, the carbon fiber recovered product was taken out from the electrolytic solution.
The method of claim 1 further comprising the step of:

(D) After the surface of the carbon fiber recyclate is filled, the water is washed to remove the cement-based inorganic rubber, wherein the pore spacing is greater than 0.1 mm, the water flow pressure is higher than 0.1 MPa, and the rinsing time is not less than 3 seconds.
The method according to claim 1, wherein the electrolyte further comprises 1.0 g/L to 5 g/L of a catalyst, wherein the catalyst is selected from the group consisting of hydrocyanic acid, carbonic acid, hydrofluoric acid, hydrosulfuric acid, and hypochlorous. A group consisting of acid, nitrous acid, nitrous acid, metasilicate, and soluble organic acids.
The method according to claim 2, wherein the electrolyte further contains 1.0 g/L to 5 g/L of the catalyst, wherein the catalyst is selected from the group consisting of hydrocyanic acid, carbonic acid, hydrofluoric acid, hydrosulfuric acid, and hypochlorous. A group consisting of acid, nitrous acid, nitrous acid, metasilicate, and soluble organic acids.
The method according to any one of claims 1 to 4, wherein the reaction temperature is from 25 ° C to 75 ° C.
The method according to claim 5, wherein the reaction temperature is from 60 ° C to 75 ° C.
The method according to claim 1, wherein the electrolyte contains a soluble hydrochloride of 0.5 to 3% by weight and a catalyst of 1.0 g/L to 5 g/L, wherein the catalyst is selected from the group consisting of hydrocyanic acid. A group consisting of carbonic acid, hydrofluoric acid, hydrosulfuric acid, hypochlorous acid, nitrous acid, nitrous acid, metasilicate, and soluble organic acid, and the reaction temperature is controlled to be 25 ° C to 75 ° C.
The method according to claim 1, wherein the electrolyte contains 0.5% to 3% by weight of soluble hydrochloride and 1.0%/L to 5 g/L of the catalyst, wherein the catalyst is selected from the group consisting of hydrocyanide. The reaction temperature is controlled to be 60 ° C to 75 ° C in the group consisting of acid, carbonic acid, hydrofluoric acid, hydrosulfuric acid, hypochlorous acid, nitrous acid, nitrous acid, metasilicate and soluble organic acid.
An electrolyte for recovering high performance carbon fibers from an inorganic cementitious material, characterized in that it contains at least:

a soluble hydrochloride salt in a weight ratio of 0.5% to 3%;

a catalyst of 1.0 g/L to 5 g/L, wherein the catalyst is selected from the group consisting of hydrocyanic acid, carbonic acid, hydrofluoric acid, hydrosulfuric acid, hypochlorous acid, nitrous acid, nitrous acid, metasilicate, and soluble organic acid. Group; and

80% to 98% water.
The electrolytic solution according to claim 9, which preferably contains 3 g/L of a catalyst.